March 2018 was characterised by significantly higher pressure than normal to the east of New Zealand. This pressure pattern, in concert with the decaying La Niña in the tropical Pacific, caused more northeasterly winds than usual over the country. These warm, humid air masses, combined with the remnants of the marine heatwave in the Tasman Sea, influenced higher than usual temperatures over New Zealand as well as some heavy rainfall events.
Mean temperatures were above average (0.51 to 1.20°C of average) or well above average (>1.20°C of average) across New Zealand, with isolated parts of Tasman and Southland experiencing near average temperatures (-0.50 to 0.50°C).
Rainfall was well above normal (>149% of normal) in the central North Island, the eastern North Island (south of Napier), Kapiti Coast, Nelson, south Canterbury, north and central Otago, and Fiordland. Rainfall was above normal (120-149% of normal) in Northland, the southern half of the North Island, and Tasman. Below normal rainfall (50-79%) was experienced in isolated patches of Auckland, Waikato, Bay of Plenty, East Cape, Christchurch, Dunedin, and Southland. Near normal rainfall (80-119% of normal) was observed elsewhere.
As of 31 March, soils were wetter than normal for the time of year across most of New Zealand. Soils were drier than normal in East Cape, Manawatu-Whanganui, eastern Southland, and Stewart Island.
Departure from average air temperature for March 2018.
End of month water balance in the pasture root zone for an average soil type where the available water capacity is taken to be 150 mm.